This invention facilitates the task of designing the flight deck windows for a new aircraft/cab design. The external field of view created by an airliner's flight deck windows must satisfy many regulatory and design requirements. The total amount of transparent material is generally limited because the window material is very heavy. In addition, the size of individual windows is limited due to the expense and technical challenges of manufacturing large glass panels of suitable optical quality and the increase in aircraft weight and complexity associated with transferring loads around large window cutouts.
The external visual field can be evaluated using “polar projections,” which are angle-angle plots of the limits of the solid angle that the pilots can see out of the windows. The “polar projections” are plots of the limits of the clear view area expressed in terms of coordinates representing angles left/right (azimuth) and angles up/down (altitude), measured from a line straight forward from the pilot's eyes.
During the design process, proposed window designs can be evaluated by comparing the polar projection of the proposal against the polar projection of previous designs and against the regulatory requirements, expressed in angle/angle coordinates. Calculating and plotting the polar projection for a window design is not a straight-forward geometric construction due to the following factors. Both left and right eyes of the pilot are used. The final graph is a union of the vision from both eyes. The pilot's head is rotated as the window area is scanned; therefore the origin point for each “sight ray” is continuously changing. The sight rays also are refracted as they pass through the transparency material.
When the requirements for the external visual field for a new window design are expressed as an angle-angle plot, an initial design point can be found by “reverse projection,” that is, to project the limits defined on the angle-angle plot back onto the three dimensional surface of the aircraft being designed. Due to the complicating factors mentioned above, this is a very difficult task. Previous to this invention there were two methods that could be used to accomplish a reverse projection, both entirely unsatisfactory.
The first method was trial and error: first, take an educated guess as to the shape of window edges that would produce a given polar projection, then create trial window geometry on the aircraft surface, next do a polar projection using all the rules set out above, and finally evaluate the result and iterate the process, adjusting the three dimensional geometry as necessary. This method is very laborious, time consuming and, due to the number of iterations required, inefficient and ineffective for optimizing the window shapes.
The second method was to create 3D surfaces radiating from an eye point to represent the desired angle-angle criteria. This set of surfaces would be intersected with the aircraft surface to create curves defining the edges of windows. Unfortunately, a simple geometric construction cannot account for the moving eye points and light refraction through the transparencies. Therefore this method is inaccurate, and the inaccuracy is more acute for windows that are not planar, yet this is a method previously used at Boeing and elsewhere to create window geometry during initial flight deck design.